Inductive device



Filed Jan. 28, 1959 Feb. 12, 1963 J. POPA 3,077,570

INDUCTIVE DEVICE 3 Sheets-Sheet 2 Feb. 12, 1963 J. PoPA 3,077,570

Filed Jan. 28, 1959 5 Sheets-Sheet 3 www 11.

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3,077,570 Patented Feb. 12, 1963 United States Patentl Ctice 3,077,570 INDUCTEVE DEVICE `lohn Pupa, Fort Wayne, ind., assigner to Generai Electric Company, a corporation of New York nnen ran. as, i959, ser. No. masas 7 Claims. (Cl. 336-61) This invention relates to inductive devices, and to magnetic cores for inductive devices, and more particularly to inductive devices such as are used for ballasting mercury vapor lamps, and to laminated magnetic cores therefore, and to improvements therein.

v Cores or the multiple coil type transformers, having one or more separate coils, are generally constructed in laminated form, with each lamination layer being formed of tw-o or more pieces to constitute a magnetic circuit. One common form of lamination layer comprises a pair of'E and l-shaped laminations; the E-shaped lamination contains tWo outer legs and an inner leg joined by a cross bar at one end; the open end of t-he E-lamination is closed, when-assembled, by the generally I-shaped lamination.

Such laminations are generally punched from metal a-re made be a minimum, and that the percentage of scrap or loss of 'strip material from which the core laminations are punched is also at a minimum. When it is realized that cores of this type are made by the hundreds. o f thousands, it will be appreciated that such savings are highly important. Y

4 ln the operation of mercury particularly those utilizing the constant-wattage or stabilizedprinciple of operatiomportions of the core may be operated at such high flux densities that the core exceeds the temperatures approved by the Underwriters Laboratory. Reducing the temperature may be acco1nplished by increasing the amount of iron inthe non# critical operating portions of the magnetic circuit in order to reduce the flux density therein. Unfortunately, this procedure when used alone is.wasteful of materials and, as implied above, transformer manufacturers are guided largely by considerations of cost.

Mercury vapor lamp transformers or ballasts are normally of relatively small size, and are of the' dry-type as distinguished from oil -filled transformers. Such drytypetransformersfare normally Aencased in an outer enclosure in a potting compound, sucli as asphalt and silica or like compound.

. A core lamination construction which would alleviate this core heating problem encountered in certain of the mercury vapor lamp transformers would therefore be desirable'. "i

An object of the invention is to provide an improved magnetic core for use in an vinductive device. i

A further object is to provide lan inductive device with improved cooling means.

, `A further object is the provision ofimproved E and I-shaped laminations for a magnetic core.

Another object of the invention is tov provide acore ofthe type described wherein the laminations are so formed 'that they may be stamped out of strip material with a minimum yof waste and a maximum utilization of the strip material in the magnetic circuit.

Briefly stated, an E-l type of laminated transformer core is provided with cooling tintes byl the periodic reyersal of one or a plurality of the E-laminations which have one outer leg wider than the other, thereby forming the `cooling utes. The laminations of the core are formed by punching the laminations fro-rn a strip of material, two E-lamiuations being formed simultaneously.

vapor lamp transformers, y

According to a preferred embodiment, the Wider outer leg of the E-lamination and the center leg of the E-lamination are equal in width to each other and to the window widths of the core. The formation of the wide outer leg and the center leg during punching causes the formation of the windows in the adjacent E-lamination. The nar power outer leg is equal in length to the wide outer leg plus the width of the cross bar of the E-lamination.

The l-laminationsare also punched from a strip of sheet material. When assembled, 'the l-laminations butt against the inside edge of the narrow outer leg and rest on the top of the wide outer leg to complete the magnetic circuit.

Such a transformer core is stacked for example, with the primary and secondary winding spaced apart and having a magnetic shunt therebetween. The laminations may be arrangedso that one or more bridged air gaps are aligned therethrough. Furthermore, the I-member may consist of a straight bar or may contain' an oiset center portion thereby resulting in an air gap; a combination of these types of I-members may be used in a single core, if desired, to produce desired reluctance paths.

4The invention together with additional objects and ad# vantages thereof will be best understood from the followingdescrip'ti-on of specific embodiments, when read in connectionv with the accompanying drawings, in which: .p ,-FIG. l is a pictorial Viewv of anassernbled laminated core according to one embodiment of the invention;` 1 1 FiG.. 2..is an exploded pictorial view of a core-illustrating the inter-relation of the reversed core laminations;

FIG. 3 is an elevation view, in section, illustrating the core assembled with the coils; j

FIG. 4 is a plan view, partly in section, illustrating ythe potted transformer;

FIG. 5 is a plan view of the layout of the E-laminations as they are punched from the strip of the material; and

FiG. 6 is a plan view of the layout of one embodiment of I-laminations as they are punched from the strip of material.

Referring to FIG. l, there is illustrated a core 1 composed of laminations 1a, 1b, 1c, etc., according to the instant invention arranged in a plurality of adjacent groups 2 forming a series of cooling utes 2' extending outwardly therefrom. Each cooling flute is composed of a group 2 of laminations in aligned position; adjacent groups of laminations lare reversed with respect to each other, as hereinafter more fully described, thereby forming the respective cooling flutes 2' on each side of the clore.. The stack of laminations may be held together by through bolts 3 and angle members 4. A series of bridged air gaps S may, if desired, extend through a leg of the core.

Referring to FIG. 2, each layer of laminations in cludes an E-mernber l6 or 7 and an I-member 8 or 9. Each E-larnination 6, 7 comprises a wide outer leg 10, 11 and a center leg 12, 13 of substantially the same width and of the same width as the space or window between the legs. As more 4clearly indicated, by distance d, FIG. 5, each tti-lamination o, 7 also contains a narrow outer leg llt, l5 of substantiallyl less width than the other or wide outer leg l0, 11, orvthe center leg 12, 13, as indicated by distance X, FIG. 5. X may be, for example, equal to d/Z; however, X is not limited to this dimension. Each E-lamination also contains a cross member i6, i7 integral with the outer legs and center leg. As previously stated, each E-lamination, 6, 7 may contain one or more bridged air gaps 5; in such a case it will be noted that in alternate reversed groups of laminations, the bridged air gaps 5 are likewise in a reversed position so that in lamination 6 the bridged air gaps 5 are at the end of the center leg 12 remote from the cross member 16, and in laminations 7 the bridged air gaps 5 are at the end of the center leg 13 nearest the cross member 17. ln this manner, as most clearly `seen in FIG. 2, the bridged air gap of the respective g-roups of laminations will `be aligned (after assembly into a core) so that they form a single passageway therethrough. The narrow leg of each E-lamination has a recess 1S (FIG. 5) on its inner face at the end remote from the cross member; the recess 1S comprises an inner face 19 and a shoulder in line with the end edges of the wide outer leg and the center leg, the purpose of which will hereinafter be explained.

Each layer of laminations also has an l-member associated with the E-lamination. The I-lamination may consist of a straight bar 9, FIG. 2; or may consist of a bar lhaving a recessed or off-set center portion 21. The I-member rests on the shoulder 20 of its associated E-lamination, butting against the inner face 19 of the recess 18. The other en-d of the l-lamination overlaps and butts against the end edge of the wide outer leg. Where an I-lamination having an off-set portion 21 is used, au air gap 22 is formed with the center leg; if a straight bar is used for the l-rnember 9, FIG. 2, then no air gap is formed. As assembled core 1 may consist of I-members each havin-g an olf-set center portion 21; or may consist of Imembers each comprising a single bar 9, FIG. 2; or alternate rever-sed groups of laminations may comprise alternate forms of lmembers so that (as illustrated in FIG. 2) each assembled core contains both forms of I- members. In this manner, the desired reluctance may be interposed in the magnetic circuit of the core.

Referring now to FIG. 3 which illustrates the core and 'Winding assembly of a transformer according to the instant invention, the transformer includes a core assembly 1 having a primary winding 23 and a secondary Winding 24 around the -center legs of the E-laminations and extending through the windows or open spaces of the E- laminations. As illustrated, to -increase the reactance of the transformer and thereby to limit the current flow to the lamp by the transformer, the primary winding 23 is spaced apart from the secondary winding 24 and a magnetic shunt 25 is placed at least partially between the respective coils, as is well known in the art. The magnetic shunt 25 comprises a rectangular stack or bar of magnetic laminations and fills a portion of the window space of the laminations between the coils.

Transformers of the size employed in mercury vapor lamps are commonly, but not necessarily, potted in an enclosing case as illustrated in FIG. 4. Such a potted transformer comprises the core assembly 1, the primary winding 23 (not shown in FlG. 4) and the secondary winding 24 within an enclosure 26 and held in place with electrical insulating or potting compound 27 such as the heretofore mentioned asphalt and silica. Leads 28, 29 and 30, 31 of the primary winding y23 and the vsecondary winding 24 respectively are passed through an opening or aperture 32 in the enclosure 26.

Transformers, according to the instant invention, were built and compared in operation to 'similar transformers without the cooling tlute's. It was found that the cooling flutes in air provided la 6% reduction in the maximum core temperature, a 12% reduction in the primary coil ,temperature rise, a 12% reduction in the secondary coil temperature rise, and a 14% reduction in copper (through permissible smaller gauge wire) and a 34% reduction in the gross weight of magnetic material (as hereinafter explained). The cooling utes in potting compound provided a 26% reduction in the primary coil temperature rise, a 27% reduction in the secondary coil tem erature rise, a 14% reduction in copper needed and a 4% reduction in the gross weight of magnetic material needed (as hereinafter more fully described). The core temperature of the potted transformer was not measured. From this analysis, it is apparent that the cooling flutes according to the instant invention yshow a significant improvement in the cooling of the transformers in both air and potting compounds.

For maximum utilization of the sheet material from which the laminations are made, a pair of E-laminations for each of the adjacent groups is formed end-for-end with respect to each other and positioned on the sheet material so that the wide outer leg and the center leg of each E-lamination substantially ills the window of the cooperating E-lamination so that the formation of the center leg and wide outer leg of one E-lamination form the Window of the cooperating lamination; that is, the windows in the cooperating lamination are formed by the removal of these legs. The narrow leg of each lamination extends along the outer edge of the strip. It is readily appreciated that the width of the windows and the Width of the wide and center legs of the E-laminations must be equal. This arrangement results in substantially no waste (except, of course, for the material removed from the bridge air gap and -bolt holes) resulting in a reduction of 34% in the gross weight of the strip material needed for the punchings over the corresponding prior core without the ilutes.

FIG. 6 illustrates the formation of one form of I-member from a lstrip of sheet material. It is noted that an elevation 33 oc-curs on the outer edge of the I-lamination opposite the off-set portion so that the l-lamination is of substantially constant cross-section. As is appreciated, the width of the I-lamination is equal to the width of the cross mem-ber of the E-lamination; in this way the narrow outer leg of the E-lamination, which is punched out in length equal to the length of the wide outer leg plus the width of the cross member, is also equal in length to the length of the wide outer leg plus the width of the I-lamination. The formation of the elevation and oit-set in one I-rnember forms the oil-set and elevation of the respective adjacent punchings.

To form a transformer and core assembly, prewound primary winding 23 and secondary winding 24 are held in proper relationship with desired magnetic shunts 25 therebetween. The alternate groups 2 of E-laminations are stacked with their narrow and wide outer legs respectively aligned and may then be assembled with the coils by passing the center leg of one group of E-laminations through center openings in the windings. Adjacent groups of E windings are assembled from opposite `sides of the coil arrangement with the wide outer legs of one group reversed with respect to the wide outer legs of the adjacent group. Groups of I-laminations are assembled with the E-laminations. After the core has been formed, the angle members 4 are assembled and the core is bolted together with through bolts 3. 'The transformer may be used in air, or, where desired, it may be potted in an enclosure 26; With the core and coil assembly within the enclosure, the enclosure may be filled with potting compound 27, such as hot asphalt and silica, to securely retain the assembly within the enclosure.

As will b'e readily appreciated, the construction according to the Ainstant invention results in reduced flux density in the cooling utes. Since the wide outer legs of the E-laminations are equal to the central leg in width, and the narrow outside leg is equal, for example, to 1/2 the width of the center leg, the narrow and wide outer legs, when adjacent to each other, have an average width of 3%: the central leg width. If 1/2 the total ,-flux of the central leg branches out into each of the outer legs, outer egs having 2%: the area of the central leg will result in a flux density in the outer leg of the ilux density in the central leg.

The reduced flux density in the outer legs, when the central leg is operating in the saturating region, is extremely effective in reducing core losses and core heating, and when combined with the cooling llutes, is very effective in cooling the core.

In accordance with the patent statutes, I have described what at present are considered to be the preferred embodiments of my invention. However, it will be obvious to those skilled in the art that various changes and modiications may be made in the disclosed structure without departing from my invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent in the United States is:

l. A magnetic core for an inductive device comprising a plurality of adjacent groups of layers of E and I-shaped laminations, each E-shaped laminations having a center leg, a wide outer leg, and a narrow outer leg, the E-laminations of each group having their narrow and wide outer legs respectively aligned, and cooling flutes formed on said core by the reversal of adjacent groups of laminations with respect to the wide and narrow outer legs of each group whereby the center leg of all of said E-laminations are aligned and the wide outer legs of one group extend outwardly beyond the narrow outer legs of the adjacent group.

2. An inductive device comprising, in combination, a magnetic core according to claim 1, and at least one winding on said center leg.

3. A magnetic core for an inductive device consisting of a plurality of adjacent groups of layers of E and I- shaped laminations, each E-shaped lamination having a center leg and a wide outer leg of the same width, and a narrow outer leg, the legs forming windows therebetween of substantially the same width as said center leg and said wide outer leg, said E-shaped laminations of each group having their narrow and wide outer legs respectively aligned, and cooling llutes formed on said core by the reversal of adjacent groups of laminations with the respect to the wide and narrow outer legs whereby the center leg of all of said Elaminations are aligned and the wide outer legs of one group extend outwardly beyond the narrow outer legs of the adjacent group.

4, A. magnetic core according to claim .3 wherein the narrow outer leg is about one-half the width of the wide outer leg.

5. A magnetic core for an inductive device consisting of a plurality of adjacent groups of layers of E and I- shaped laminations, each E-shaped lamination having a center leg, a wide outer leg and a narrow outer leg, the E-laminations of each group having their narrow and wide outer legs respectively aligned, the narrow outer leg being equal in length to the length of said wide outer leg plus the width of the I-shaped lamination and having a shoulder therein in line with the end edges of the wide outer leg and center leg, said I-shaped lamination having one end resting on said shoulder and butting against the inside edge of said narrow leg and having its other end overlapping and butting against the end edge of the wide outer leg and cooling llutes formed on said core by the reversal of adjacent groups of laminations with respect to the wide and narrow outer legs of said E-shaped laminations whereby the side legs of one group extend outwardly beyond the narrow legs of the adjacent group and provided a reduced linx density during operation as compared with the ilux density of said narrow legs thereby effectively minimizing the core losses when said center leg is operated in the saturating region.

6. A magnetic core according to claim 5 wherein the said I-shaped laminat-ion is of uniform cross-section and contains a recessed center portion whereby an air gap is formed between said I-shaped lamination and said center leg.

7. A magnetic core according to claim 5 wherein said narrow outer leg is about one-half the width of the wide outer leg.

References Cited in the tile of this patent UNITED STATES PATENTS 1,623,345 Hopkins Apr. 5, 1927 2,137,433 wirz Nov. 22, 193s 2,330,824 Granada ooi. 5, 194s 2,451,202 Comstock ooi. 12, 194s 2,947,957 Spindler Aug. 2, 1960 

1. A MAGNETIC CORE FOR AN INDUCTIVE DEVICE COMPRISING A PLURALITY OF ADJACENT GROUPS OF LAYERS OF E AND I-SHAPED LAMINATIONS, EACH E-SHAPED LAMINATIONS HAVING A CENTER LEG, A WIDE OUTER LEG, AND A NARROW OUTER LEG, THE E-LAMINATIONS OF EACH GROUP HAVING THEIR NARROW AND WIDE OUTER LEGS RESPECTIVELY ALIGNED, AND COOLING FLUTES FORMED ON SAID CORE BY THE REVERSAL OF ADJACENT GROUPS OF LAMINATIONS WITH RESPECT TO THE WIDE AND NARROW OUTER LEGS OF 